The objective of this project is to elucidate the relationship between molecular composition and topographic arrangements of membrane building blocks with reference to plasma membrane functions. Bioelectrogenesis, transport, and many metabolic phenomena are based on the proper associations of membrane proteins and lipids. In particular, the function of membrane ecto-enzymes has been the objective of this study. We have found that these phosphoesterhydrolases are part of a regulatory system involved in traumatic shock. A self-sustaining increase in extra-cellular ATP is proposed as the biochemical lesion in shock. Molecular probes are used to modify plasma membranes of intact cells of CNS-derived tissue cultures. Modified membranes are used to elucidate the chemical composition of enzyme active sites and also associations with membrane lipids. Synaptosome-like vesicles released from cell cultures have a lipid composition distinct from parent cells.